The present invention relates to magnetic bearings; wherein the stator and rotor are separated from each other by magnetic flux fields that attract the rotor to the stator in both the radial and axial directions; and more particularly, to a magnetic bearing system and related methods.
In any rotating machine, the turning elements, otherwise defined as rotors, are physically separated from the non-turning or stationary elements, sometimes referred to as stators, to prevent damage of the rotors or the stators. This separation is accomplished by use of bearings which may act in a radial direction, that is perpendicular to the essential axis about which turning occurs, and also in the axial direction, that is along the axis about which turning occurs.
Machinery characteristics come in part from the balance of the rotors, but even when a rotor is brought into perfect balance, other dynamic characteristics may still produce undesirable running characteristics. These latter characteristics stem from the dynamics of the system which may be described in terms of the masses and their distributions, damping properties of the materials of construction, configurations of the design, and the stiffnesses of the various components and their interactions. Included in these above-noted parameters are the bearings that support the rotating elements, which rotating elements taken together may be simply referred to as the rotor.
Rotating machines, such as pumps and compressors for example, display operating characteristics which come in part from such bearing parameters. With the use of magnetic bearings, these parameters may be controlled or modified as the rotor is stationary or turning. In general, conventional fluid film bearings or so-called anti-friction bearings, cannot be adjusted or modified either when the rotor is stationary, nor when it is turning in the bearings. So magnetic bearings offer many advantages over the more conventional bearings.
For example, by varying the defining parameters of the bearings, the overall system dynamics may be controlled. With magnetic bearings, these parameters may be adjusted or changed when the rotors are running (i.e., turning with the bearings) or even when they are in support but not turning. It is important to understand that support is not usually attained in a fluid film bearing until the rotor is turning. Such is not the case with the magnetic bearing; it may be in support whether the rotor is turning or not.
The basic elements of a rotating machine are noted in FIG. 1. The rotor includes a multiplicity of masses distributed along a flexible shaft, or in some designs, the flexible shaft is replaced by a series of equivalent rings or cylinders that connect the masses to one another. The individual magnetic bearings are arranged to carry either radial loads or axial loads or both and are attached to the stator or what is frequently called the frame or housing of the machine. In addition, most designs call for some type of back-up bearing that comes into service when the rotor is not turning and the magnetic bearings are not activated or in the situation in which the rotor motion becomes large and contact is likely to occur between the rotor and stator. "Large" motion means a few thousands of an inch as the space or clearance between the face of a magnetic bearing, which is attached to the housing, and the rotor element adjacent to the face is typically a few thousandths of an inch and contact between these two areas is not desirable.
Magnetic bearing systems may be used in applications where the control system will be expected to perform correctly for years without failure. Further, because of close tolerances and the desirability of using magnetic bearings for high speed apparatus, it is important that such a system provide for smooth operation at higher and higher critical speeds.
Multiprocessors offer many desirable properties such as significant system throughput; and the potential for fault tolerant performance. The incorporation of fault tolerance in multiprocessors is typically accomplished through the inclusion of fault detection and location routines and redundant processing modules. As advances in VLSI component technology allow processor performance to increase with corresponding reductions in cost, size, and power consumption, multiprocessor systems will be much more widely used because of their inherent advantages.
Unfortunately, the benefits associated with multiprocessor architectures are not easily attained because the partitioning of general computing tasks is quite a difficult problem [1]. In general, extraction of the parallel components of most algorithms is very difficult. Also, once an algorithm has been converted to a parallel form, optimal assignment of processing elements is difficult. Finally, fault-tolerant systems that employ software intensive fault detection, location, and recovery techniques can spend a significant amount of processing time executing self-diagnostic routines. In real-time systems, this overhead may reduce system throughput to an unacceptable level.